Two examples of costly sociality from Alcock 1998 Sociality and Altruism Sociality and Social Behavior Ovicidal female Broadly-defined: any non-solitary behavior acorn woodpeckers Overview: The Spectrum of social behavior, broadly defined: •Some costs of social behavior •From “simple” conspecific interactions such as •Imply importance of demonstrating benefits encounters between territory owners and intruders •To highly organized eusocial systems (honeybees) •Assumption of genetic basis •Direct selection, Indirect selection Human bias in thinking about social systems: •Types of social interaction in terms of costs/benefits •Highly organized social behavior and social living are “more evolved” in some way •Mutual versus Selfish versus Altruistic behaviors •This is a bias because it is what we do •Explaining altruistic behavior •Nothing says evolution should proceed toward greater social organization •Quick dispatch of Group Sel’n and Recip. Altru. •Kin Selection •Social Organization may incur high costs: Parasite-harboring cliff-swallows •Inclusive fitness •Hamilton’s Rule •Bottom Line: To explain social living and social behavior you must be very clear about the fitness benefits of sociality to individuals

Recalling the Genetic Cost/Benefit classification of Explaining Altruistic Behavior Perspective social behaviors THE BIG QUESTION: How could a behavior Big assumption underlying the evolutionary Social behaviors can be characterized as which reduces the fitness of an individual ever ecology perspective on social behavior: interactions between “Self” and “Neighbor” •Behaviors in question have a genetic basis •Four main types based on cost or benefit to self evolve in a population? •For behaviors to increase in frequency in populations or neighbor: the genes controlling them must make it to future THREE PROPOSED EXPLANATIONS: generations at a higher than average rate Effect On Neighbor 1. Group Selection (a largely discredited •How do these behaviors “help those genes along” to the hypothesis) next generation? Imagine an individual named Fred: +– (a) Direct Selection: Fred’s genes make him behave in such a way as to increase the chances of passing on his Mutually 2. Reciprocal Altruism (a game theoretic genes (i.e. of having more offspring) OR in such a + Beneficial Selfish notion with little empirical support) way as to increase the chances of Fred’s offspring surviving to pass on their genes. 3. Kin selection (a fairly widely-accepted This promotes the direct fitness of the genes Mutually influencing Fred’s behavior Altruistic Disadvantageous hypothesis based on genetic arguments and

Effect On Self – (b) Indirect Selection: Fred’s behavior promotes the indirect selection) fitness of individuals who are not his offspring, BUT those individuals happen to carry copies of Fred’s genes (because they may share a common ancestor) • MB and S are easily explained via natural selection This leads to indirect fitness benefits. • MD ought not be very frequent • Altruistic behavior is the tough one to explain

Note: Altruistic behavior doesn’t mean “consciously altruistic” as in “Oh! You’re such an altruist!” A Brief History of Group Critical Reassessment of Before getting to kin-selection, however, we investigate Reciprocal Altruism Selection Group Selection (Trivers) Reciprocity: a mechanism by which altruistic behavior Basic Premise of Group Selection: the Wynne-Edwards (early 1960’s) stimulated a great deal of might be maintained by increasing the direct fitness of the “evolutionary battleground” is the space of all separate criticism of group selection individual behaving altruistically populations (groups) of organisms. The “winners” and “losers” in this evolution match are the populations Oddly, Wynne-Edwards was a great proponent of GS Direct Fitness is increased because the recipient of the (groups) themselves. •Natural Regulation of Population size altruistic behavior “returns the favor later” •“Saw its (GS’s) magnificent consequences so “You rub my back and I’ll rub yours” Contrast to Individual Selection within a population universally that evolutionary ecologists were forced to consider the argument more carefully.” --Ricklefs Requires that the cost for the giver is less than the benefit The first Group-Selection Argument was formed by for the recipient Darwin in his On the Origin of Species to explain features Huge Backlash!! of sterile worker bees: Problem: Single or Few Interactions: Game theory shows How could features of “good” sterile workers be Criticisms of Group Selection: cheaters can easily invade a population of reciprocators: acted upon by natural selection if they don’t leave any 1. Most organisms don’t organize themselves into “You rub my back and I’ll say I’ll rub yours, but I’ll really offspring? groups the way that they would have to for Group leave town before I do” Selection to be effective Darwin: “By the survival of communities with females 2. The time scale for group selection is slow---much Possible Solution: Repeated interaction makes it harder to which produced most neuters having the advantageous slower than for individual selection within cheat successfully. modification, all the neuters come to be thus populations. Group selection should be overwhelmed characterized.” by selfish behavior. Does reciprocity occur? Very few examples This was a widely accepted idea, adopted for many Hamilton (1964) and Maynard Smith (1964) proposed kin- Wilkinson (1984) and vampire bats explanations in evolutionary ecology for many years...until selection which has essentially replaced group selection the early 1960’s. thinking.

And now: Imagine you are a contestant on the The Theory of Kin Selection Kin Selection Game Show The Rules: Kin Selection: A process whereby altruism may be •You are the contestant selected for in a population because it increases the •You are a diploid organism inclusive fitness of the individual doing the altruistic •two copies of the “locus in question” behavior •You score points by “putting individuals into a population” •You get one point for each gene in those individuals that is a copy of one of your genes at the “locus in question” •Your plays are choices between 2 alternatives

Wilkinson’s data Example: Choose between from vampire bats (a) putting 50 offspring (from matings with individuals unrelated to you) into the population suggests reciprocal (b) putting 100 individuals that aren’t related to altruism in giving you into the population food (blood meals) reciprocally Belding’s Ground Squirrel between individuals A tougher one: Choose between (a) 10 offspring (from matings with individuals in a group. unrelated to you) (b) 10 full-brothers (i.e. ten more offspring of There are few other both of your parents) examples, though Back to the Game Show: Choose between Surprise: In the second case, the expected gain in points How about r between two full siblings (a) 10 offspring (from matings with individuals Ma Pa is the same for choice (a) and (b). unrelated to you) 12 3 4 (b) 10 full-brothers (i.e. ten more offspring of both of Why? To understand why we need a few more concepts. your parents)

Identity by Descent: two genes are said to be identical by descent if they are copies of the same ancestral gene Either choice a or b will give you 5 points. 1 3 14 23 24 Coefficient of relatedness (r): the coefficient of How about: relatedness between two individuals is the expected (a) 4 full brothers proportion of their genes which are identical by descent (b) 4 uncles and 16 first cousins? 4 Possible Genotypes in the Siblings Example: r between a parent and an offspring Probability 1/4 for each.

Parent A Parent B Now Consider the Expected Proportion of IBD Coefficients of Relatedness o o between say o o 13 Relationship of Self to: Coeff. of Rel. (r) Self 1.0 One gene from and a randomly chosen One gene from Offspring or Parent 0.5 Parent A Parent B sibling. Full Sibling 0.5 o o = (.25)(1) + (.25)(.5) + (.25)(.5) + .25(0) = .5 Half Sibling 0.25 Uncle/Aunt or 0.25 Nephew/Niece So, r between two full siblings is 0.5 Grandparent or 0.25 Half of the offsprings genes are from either Grandchild parent. Hence r = 1/2. First Cousin 0.125

Back to Biology: The points in the gameshow are Hamilton’s Rule measured in the units of inclusive fitness of your genes Hamilton’s Rule: an altruistic behavior may be Inclusive Fitness = Direct Fitness + Indirect Fitness adaptive if it results in positive inclusive fitness. = (Survival of offspring) x (r for parent-offspring) + (Survival of non-descendant kin) x (the proper r for each Numerical Example: You save the lives of 5 nephews, type of relationship) but in doing so you lose the opportunity to produce two sons. Example calculation of inclusive fitness: Imagine you have 29 offspring. Through your diligent parental care 15 Inclusive fitness = -2(.5) + 5(.25) = .25 survive to reproduce. 5 survive even though you neglected Conclusion via Hamilton’s rule: this could be adaptive them. You give your life in an heroic deed that saves the lives of 8 cousins, 4 nephews and 2 half-sibs who would have died if you hadn’t saved them. Reyer (1984) Your inclusive fitness is: Pied Kingfisher (5 + 15)(.5) + 8(.125) + 4(.25) + 2(.25) = 10 + 2.5 = 12.5 Study Altruism and Inclusive Fitness: altruistic behaviors have costs which are reductions in direct fitness but if they benfit See the reading relatives, the indirect fitness benefits to the altruist may from Alcock for offset the direct fitness costs. details.